1. Field of the Invention
The present invention relates to a clamp of the type that rotates a clamp rod.
2. Explanation of Related Art
There is a conventional technique of the rotary clamp of this type which is constructed in the following manner, as disclosed in U.S. Pat. No. 5,820,118.
A clamp rod is inserted into a housing, an upper wall of which supports a halfway height portion of the clamp rod vertically movably. The clamp rod has a lower portion provided with a piston which is supported by a barrel portion of the housing vertically movably.
The conventional technique has the following problem.
A fitting gap between an outer peripheral surface of the piston provided at the lower portion of the clamp rod and the barrel portion of the housing. Therefore, when driving the clamp rod for clamping, the fitting gap inclines the clamp rod although only slightly to result in the impossibility of guiding the clamp rod with a good accuracy.